A honing machine is commonly used for finishing a bore in a workpiece. When a workpiece, such as a cylinder, is bored out, the boring tool leaves V-shaped grooves in the surface of the cylinder wall, much like those on a phonograph record. The sharp peaks of these ridges are rounded off by honing the bore. The typical honing machine uses a set of honing tools spaced around a machine head and fed progressively outwardly against a generally cylindrical internal wall of a workpiece while the machine head is simultaneously rotated within and reciprocated along the workpiece. In this manner, the working face of each honing tool is forced into engagement with the wall under selected honing pressure to abrade and finish the wall.
The specific honing tools usually include a honing element secured in a holder. This honing element is commonly a one-piece element, and in fact is usually referred to as a "honing stone". Examples of such honing elements are described in prior U.S. Pat. Nos. 3,829,299; 2,980,524; 3,352,067; 3,154,893; 3,132,451; 4,528,776; 4,555,875; 3,972,161; and 3,918,218. In the latter two patents, a plurality of cutting filaments are embedded in a matrix, however the resulting honing element is nonetheless a one-piece relatively rigid element.
In the course of honing, it is common for chips or burns to be knocked loose from the cylinder. Because of the solid structure of most honing elements, no clearance is present between the wall and the working face of the honing element. These chips may wedge themselves between the working face of the honing element and the wall. Although a liquid is usually flushed through the bore during honing, such has little effect on the wedged chips. Eventually, either the wall or the honing element must give, resulting in the damage of a honing element or stone and/or the scarring of a bore of what may be an expensive cylinder.
It is also not uncommon for a rigid honing tool to embed a hard abrasive grain in the surface being honed. If this contamination occurs, excessive piston ring wear results, which in an internal combustion engine leads to "blow by" which results in environmental problems.
Also many bores such as engine bores have lateral ports. Conventional honing stones or tools cannot radius or finish the edges of such ports. Thus a need remains for an improved honing tool providing improved surface finish.
During recent years, to correct these problems and to improve upon the final finishing results, a second honing head was added to a few high production automotive engine block lines directly after the rough and finishing honing operation. The honing tools used were superabrasives plated on very fine wire filaments, lightly filled, and fine abrasive nylon brushes. Results of this added operation have been questionable based upon quality improvements and economic justification.
A second head brush hone using very fine spaced bristles may be seen in European Patent Publication 0 247 572. A post hone brushing machine is also seen in U.S. Pat. No. 5,042,202. In U.S. Pat. No. 4,980,996 there is illustrated a machine using tufted spaced bristles in combination with a high pressure spray or jet to remove metal nap after honing. In a related patent, an option of using bristles in ring holders is disclosed as seen in U.S. Pat. No. 5,085,014.
Also recently used in post honing second station operations are honing tools of the type shown in the parent application of Scheider and Warner, Ser. No. 07/508,060, entitled "Abrasive Filament Honing Tool And Method Of Making And Using The Same", filed Dec. 14, 1989. The tool of this copending application comprises tightly packed nylon-abrasive filaments which form a dense and compact slightly yieldable face. Such tool has been performing adequately in post honing, second station operations to improve honed surfaces.